With a continuous increase in bandwidth requirements of users and support from broadband strategies of governments of various countries, passive optical networks (PON) are massively deployed around the globe.
Generally, a PON system includes an optical line terminal (OLT) located in a central office, multiple optical network units (ONU) or optical network terminals (ONT) located at a user side, and an optical distribution network (ODN) used to perform multiplexing/demultiplexing on an optical signal between the optical line terminal and the optical network units. The optical line terminal and the optical network unit perform upstream and downstream data transceiving by using optical modules disposed in the optical line terminal and the optical network unit. Because a Gigabit passive optical network (GPON), an Ethernet passive optical network (EPON), a 10GPON, or a 10GEPON that is currently deployed or is being deployed is a single-wavelength system, that is, there is only one wavelength in an upstream (a direction from the ONU to the OLT is referred to as upstream) direction and a downstream (a direction from the OLT to the ONU is referred to as downstream) direction, an upstream bandwidth and a downstream bandwidth are shared by multiple ONUs, limiting bandwidth improvement of each ONU. For ease of description, the following ONU is an alternative name of an ONU and/or ONT.
To improve a transmission bandwidth of a same fiber, the International Telecommunication Union Telecommunication Standardization Sector (ITU Telecommunication Standardization Sector, ITU-T) standard organization is formulating a time wavelength division multiplex passive optical network (TWDM-PON). The TWDM-PON is a time division multiplex (TDM) and wavelength division multiplex (WDM) hybrid system. In the downstream direction, there are multiple (generally 4 to 8) wavelengths to be transmitted in a WDM manner, and in the upstream direction, there are also multiple (generally 4 to 8) wavelengths to be transmitted in a WDM manner. Each ONU may choose to receive data of any downstream wavelength and uploads data by using any upstream wavelength. Specific wavelength allocation is controlled by the OLT, and function control is mainly performed by a Media Access Control (MAC) module of the OLT. Each wavelength works in a TDM mode. That is, one wavelength may be connected to multiple ONUs, each ONU connected to a same wavelength in the downstream direction occupies a bandwidth of a partial timeslot, and each ONU connected to a same wavelength in the upstream direction uploads data in a time division manner. In the TWDM-PON, which wavelength an ONU is registered with is controlled by the OLT. Because a laser diode (LD) implementing electrical-to-optical conversion and a photo detector (PD) implementing optical-to-electrical conversion are in an optical module, which is generally a pluggable optical module such as a small form-factor pluggable (SFP), the OLT needs to use a MAC of the ONU to control an optical module of the ONU to select a particular wavelength for receiving and sending. Therefore, two problems exist: one is that complex interaction is needed between an OLT and an ONU; and the other is that an optical module cannot work independently of an ONU and an OLT, that is, an optical module used in a TWDM-PON cannot be used in another WDM scenario, for example, cannot be used as an optical module of an Ethernet switch optical port.
Another manner for improving a transmission bandwidth of a same fiber is a wavelength division multiplex passive optical network (WDM-PON). A specific structure is shown in FIG. 3. An operating wavelength of each ONU is determined by an array waveguide grating (AWG) because a wavelength passing through each AWG port is determinate, and an optical module of each ONU works at a different wavelength. In a WDM-PON, there are mainly two types of optical modules. One is that a wavelength of an optical module of each ONU is fixed, that is, an optical module is colored. In this case, N optical modules of different types are needed to deploy one WDM-PON. N is a quantity of ports of an AWG. Storage and management of optical modules are relatively troublesome. The other optical module has a tunable wavelength and is also referred to as a colorless optical module. There are multiple manners for implementing a colorless optical module. CN201010588118.2 provides a self-seeded colorless WDM-PON solution. An external cavity laser is implemented by changing an ODN structure and adding a reflector between two AWGs. Autonomous wavelength selection is directly performed by using an AWG, to select a wavelength of each ONU optical module. FIG. 4 is a tunable laser-based WDM-PON. A self-seeded colorless WDM-PON needs to modify an existing ODN network and is not suitable for a splitter-based ODN network. These splitter-based ODN networks have been deployed on a global scale and are used for GPON or EPON access routing. Allocation and management of a wavelength of a tunable laser-based colorless WDM-PON optical module are still in the charge of OLT and ONU devices. Tight coupling between the devices and the optical module limits that such colorless optical modules can be applied only to WDM-PON devices supporting wavelength allocation and management but cannot be directly used as optical modules of Ethernet switches that are already widely used.
Therefore, the prior art still cannot provide a colorless optical module, which can be directly used as an optical module of a conventional Ethernet switch or another network device already deployed.